Yep. This guy was actually pretty lucky, as he could have gotten a tranquilizer shot and wouldn't have been able to argue his point for a while. With the hospital happily charging $10k/day :)
Don't you generally have to give consent for medical treatment?
Not if they think you're mentally unstable enough to warrant them administering treatment, regardless if that treatment ends up being necessary or not.
Does that open up the possibility of suing the psychiatrist.
No they're exercising their duty of care with valid reason to believe it's the right course of action.